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https://issues.apache.org/jira/browse/LUCENE-2843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12979348#action_12979348
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Yonik Seeley commented on LUCENE-2843:
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bq. My reasoning is merely that alternative exists, and it is viable. As proven
by pretty high-profile users.
Actually, I sort of agree. I read the "in memory" too fast and didn't realize
you were talking about memory mapped.
There are other parts of sphinx that are kept directly in memory (not memory
mapped) and do limit it's single-node scalability too much IMO.
Unfortunately, Java has additional overhead wrt mmap, and you also can't do
some stuff that you could do in C. All this means is that trade-offs that made
sense for C/C++ solutions may or may not make sense for Java solutions.
> Add variable-gap terms index impl.
> ----------------------------------
>
> Key: LUCENE-2843
> URL: https://issues.apache.org/jira/browse/LUCENE-2843
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 4.0
>
> Attachments: LUCENE-2843.patch, LUCENE-2843.patch
>
>
> PrefixCodedTermsReader/Writer (used by all "real" core codecs) already
> supports pluggable terms index impls.
> The only impl we have now is FixedGapTermsIndexReader/Writer, which
> picks every Nth (default 32) term and holds it in efficient packed
> int/byte arrays in RAM. This is already an enormous improvement (RAM
> reduction, init time) over 3.x.
> This patch adds another impl, VariableGapTermsIndexReader/Writer,
> which lets you specify an arbitrary IndexTermSelector to pick which
> terms are indexed, and then uses an FST to hold the indexed terms.
> This is typically even more memory efficient than packed int/byte
> arrays, though, it does not support ord() so it's not quite a fair
> comparison.
> I had to relax the terms index plugin api for
> PrefixCodedTermsReader/Writer to not assume that the terms index impl
> supports ord.
> I also did some cleanup of the FST/FSTEnum APIs and impls, and broke
> out separate seekCeil and seekFloor in FSTEnum. Eg we need seekFloor
> when the FST is used as a terms index but seekCeil when it's holding
> all terms in the index (ie which SimpleText uses FSTs for).
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